/**
 * Copyright (C) 2002-2015   The FreeCol Team
 * <p>
 * This file is part of FreeCol.
 * <p>
 * FreeCol is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 * <p>
 * FreeCol is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with FreeCol.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.sf.freecol.server.ai.mission;

import java.util.logging.Logger;

import javax.xml.stream.XMLStreamException;

import net.sf.freecol.common.io.FreeColXMLReader;
import net.sf.freecol.common.io.FreeColXMLWriter;
import net.sf.freecol.common.model.Ability;
import net.sf.freecol.common.model.Colony;
import net.sf.freecol.common.model.FreeColGameObject;
import net.sf.freecol.common.model.IndianSettlement;
import net.sf.freecol.common.model.Location;
import net.sf.freecol.common.model.Direction;
import net.sf.freecol.common.model.PathNode;
import net.sf.freecol.common.model.Player;
import net.sf.freecol.common.model.Settlement;
import net.sf.freecol.common.model.Unit;
import net.sf.freecol.common.model.pathfinding.CostDecider;
import net.sf.freecol.common.model.pathfinding.CostDeciders;
import net.sf.freecol.common.model.pathfinding.GoalDecider;
import net.sf.freecol.common.model.pathfinding.GoalDeciders;
import net.sf.freecol.common.util.LogBuilder;
import net.sf.freecol.server.ai.AIMain;
import net.sf.freecol.server.ai.AIMessage;
import net.sf.freecol.server.ai.AIUnit;


/**
 * Mission for sending a missionary to a native settlement.
 */
public class MissionaryMission extends Mission
{

    private static final Logger logger = Logger.getLogger( MissionaryMission.class.getName( ) );

    /** The tag for this mission. */
    private static final String tag = "AI missionary";

    /**
     * The target to aim for, used for a TransportMission.
     * Either an IndianSettlement, or a backup Colony to head for before
     * retargeting.
     */
    private Location target;


    /**
     * Creates a missionary mission for the given <code>AIUnit</code>.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param target The target <code>Location</code> for this mission.
     */
    public MissionaryMission( AIMain aiMain, AIUnit aiUnit, Location target )
    {
        super( aiMain, aiUnit, target );
    }

    /**
     * Creates a new <code>MissionaryMission</code> and reads
     * the given element.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param xr The input stream containing the XML.
     * @throws XMLStreamException if a problem was encountered
     *      during parsing.
     * @see net.sf.freecol.server.ai.AIObject#readFromXML
     */
    public MissionaryMission( AIMain aiMain, AIUnit aiUnit,
                              FreeColXMLReader xr ) throws XMLStreamException
    {
        super( aiMain, aiUnit );

        readFromXML( xr );
    }


    /**
     * Extract a valid target for this mission from a path.
     *
     * @param aiUnit A <code>AIUnit</code> to perform the mission.
     * @param path A <code>PathNode</code> to extract a target from,
     *     (uses the unit location if null).
     * @return A target for this mission, or null if none found.
     */
    public static Location extractTarget( AIUnit aiUnit, PathNode path )
    {
        if ( path == null ) return null;
        final Location loc = path.getLastNode( ).getLocation( );
        Settlement settlement = ( loc == null ) ? null : loc.getSettlement( );
        return ( settlement instanceof IndianSettlement
                && invalidIndianSettlementReason( aiUnit,
                                                  ( IndianSettlement ) settlement ) == null )
                ? ( IndianSettlement ) settlement
                : ( settlement instanceof Colony
                && invalidColonyReason( aiUnit, ( Colony ) settlement ) == null )
                ? ( Colony ) settlement
                : null;
    }

    /**
     * Evaluate a potential cashin mission for a given unit and
     * path.
     *
     * @param aiUnit The <code>AIUnit</code> to do the mission.
     * @param path A <code>PathNode</code> to take to the target.
     * @return A score for the proposed mission.
     */
    public static int scorePath( AIUnit aiUnit, PathNode path )
    {
        Location loc = extractTarget( aiUnit, path );
        return ( loc instanceof IndianSettlement )
                ? 1000 / ( path.getTotalTurns( ) + 1 )
                : Integer.MIN_VALUE;
    }

    /**
     * Makes a goal decider that checks for potential missions.
     *
     * @param aiUnit The <code>AIUnit</code> to find a mission with.
     * @param deferOK Enable deferring to a fallback colony.
     * @return A suitable <code>GoalDecider</code>.
     */
    private static GoalDecider getGoalDecider( final AIUnit aiUnit,
                                               final boolean deferOK )
    {
        GoalDecider gd = new GoalDecider( )
        {
            private PathNode bestPath = null;
            private int bestValue = Integer.MIN_VALUE;

            @Override
            public PathNode getGoal( ) { return bestPath; }

            @Override
            public boolean hasSubGoals( ) { return true; }

            @Override
            public boolean check( Unit u, PathNode path )
            {
                if ( path.getLastNode( ).getLocation( ).getSettlement( )
                        instanceof IndianSettlement )
                {
                    int value = scorePath( aiUnit, path );
                    if ( bestValue < value )
                    {
                        bestValue = value;
                        bestPath = path;
                        return true;
                    }
                }
                return false;
            }
        };
        return ( deferOK ) ? GoalDeciders.getComposedGoalDecider( false, gd,
                                                                  GoalDeciders.getOurClosestSettlementGoalDecider( ) )
                : gd;
    }

    /**
     * Find a suitable mission location for this unit.
     *
     * @param aiUnit The <code>AIUnit</code> to execute this mission.
     * @param range An upper bound on the number of moves.
     * @param deferOK Enables deferring to a fallback colony.
     * @return A path to the new target, or null if none found.
     */
    private static PathNode findTargetPath( AIUnit aiUnit, int range,
                                            boolean deferOK )
    {
        if ( invalidAIUnitReason( aiUnit ) != null ) return null;
        final Unit unit = aiUnit.getUnit( );
        final Location start = unit.getPathStartLocation( );
        final Unit carrier = unit.getCarrier( );
        final GoalDecider gd = getGoalDecider( aiUnit, deferOK );
        final CostDecider standardCd
                = CostDeciders.avoidSettlementsAndBlockingUnits( );
        // Is there a valid target available from the starting tile?
        return unit.search( start, gd, standardCd, range, carrier );
    }

    /**
     * Finds a suitable mission target for the supplied unit.
     * Falls back to the best colony if a path is not found.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @param range An upper bound on the number of moves.
     * @param deferOK Enables deferring to a fallback colony.
     * @return A new target for this mission.
     */
    public static Location findTarget( AIUnit aiUnit, int range,
                                       boolean deferOK )
    {
        PathNode path = findTargetPath( aiUnit, range, deferOK );
        return ( path == null ) ? null : extractTarget( aiUnit, path );
    }

    /**
     * Prepare a unit for a Missionary mission.
     *
     * @param aiUnit The <code>AIUnit</code> to prepare.
     * @return A reason why the unit can not perform this mission, or null
     *     if none.
     */
    public static String prepare( AIUnit aiUnit )
    {
        String reason = invalidReason( aiUnit );
        if ( reason == null )
        {
            final Unit unit = aiUnit.getUnit( );
            if ( ! unit.hasAbility( Ability.ESTABLISH_MISSION )
                    && ( ( ( FreeColGameObject ) unit.getLocation( ) )
                    .hasAbility( Ability.DRESS_MISSIONARY ) ) )
            {
                aiUnit.equipForRole( unit.getSpecification( ).getMissionaryRole( ) );
            }
            reason = ( unit.hasAbility( Ability.ESTABLISH_MISSION ) )
                    ? null
                    : "unit-can-not-establish-mission";
        }
        return reason;
    }

    /**
     * Why would this mission be invalid with the given unit?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @return A reason to not perform the mission, or null if none.
     */
    private static String invalidMissionReason( AIUnit aiUnit )
    {
        String reason = invalidAIUnitReason( aiUnit );
        if ( reason != null ) return reason;
        final Unit unit = aiUnit.getUnit( );
        return ( ! unit.isPerson( ) ) ? Mission.UNITNOTAPERSON
                : ( unit.getSkillLevel( ) >= - 1
                && ! unit.hasAbility( Ability.EXPERT_MISSIONARY ) )
                ? "unit-is-not-subskilled-or-expertMissionary"
                : ( unit.isInEurope( ) || unit.isAtSea( ) )
                ? ( ( unit.getOwner( ).getNumberOfSettlements( ) <= 0 )
                ? "unit-off-map-but-missing-initial-settlement"
                : null )
                : ( unit.isInMission( ) ) ? "unit-is-already-at-mission"
                : null;
    }

    /**
     * Why would a MissionaryMission be invalid with the given Colony?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param colony The <code>Colony</code> to check.
     * @return A reason to not perform the mission, or null if none.
     */
    private static String invalidColonyReason( AIUnit aiUnit, Colony colony )
    {
        return invalidTargetReason( colony, aiUnit.getUnit( ).getOwner( ) );
    }

    /**
     * Why would a MissionaryMission be invalid with the given
     * IndianSettlement?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param is The <code>IndianSettlement</code> to check.
     * @return A reason to not perform the mission, or null if none.
     */
    private static String invalidIndianSettlementReason( AIUnit aiUnit,
                                                         IndianSettlement is )
    {
        String reason = invalidTargetReason( is );
        if ( reason != null ) return reason;
        final Player owner = aiUnit.getUnit( ).getOwner( );
        return ( ! owner.hasContacted( is.getOwner( ) ) )
                ? "target-is-uncontacted"
                : ( is.getOwner( ).atWarWith( owner ) )
                ? "target-at-war"
                : ( is.hasMissionary( owner ) )
                ? "target-has-our-mission"
                : null;
    }

    /**
     * Why would this mission be invalid with the given AI unit?
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @return A reason for invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit )
    {
        return invalidMissionReason( aiUnit );
    }

    /**
     * Why would this mission be invalid with the given AI unit and location?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param loc The <code>Location</code> to check.
     * @return A reason for invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit, Location loc )
    {
        String reason = invalidMissionReason( aiUnit );
        return ( reason != null )
                ? reason
                : ( loc instanceof IndianSettlement )
                ? invalidIndianSettlementReason( aiUnit, ( IndianSettlement ) loc )
                : ( loc instanceof Colony )
                ? invalidColonyReason( aiUnit, ( Colony ) loc )
                : Mission.TARGETINVALID;
    }


    // Implement Mission
    //   Inherit dispose, getTransportDestination, isOneTime

    /**
     * {@inheritDoc}
     */
    @Override
    public int getBaseTransportPriority( )
    {
        return NORMAL_TRANSPORT_PRIORITY;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location getTarget( )
    {
        return target;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setTarget( Location target )
    {
        if ( target == null || target instanceof Settlement )
        {
            this.target = target;
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location findTarget( )
    {
        return findTarget( getAIUnit( ), 20, true );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String invalidReason( )
    {
        return invalidReason( getAIUnit( ), getTarget( ) );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Mission doMission( LogBuilder lb )
    {
        lb.add( tag );
        String reason = invalidReason( );
        if ( isTargetReason( reason ) )
        {
            return retargetMission( reason, lb );
        }
        else if ( reason != null )
        {
            return lbFail( lb, false, reason );
        }

        // Go to the target.
        final AIUnit aiUnit = getAIUnit( );
        final Unit unit = getUnit( );

        Unit.MoveType mt = travelToTarget( getTarget( ),
                                           CostDeciders.avoidSettlementsAndBlockingUnits( ), lb );
        switch ( mt )
        {
            case MOVE:
                // Reached an intermediate colony.  Retarget, but do not
                // accept fallback targets.
                lbAt( lb );
                Location completed = getTarget( );
                Location newTarget = findTarget( aiUnit, 20, false );
                if ( newTarget == null || newTarget == completed )
                {
                    return lbFail( lb, false, "retarget failed" );
                }
                setTarget( newTarget );
                return lbRetarget( lb );

            case MOVE_HIGH_SEAS:
            case MOVE_NO_MOVES:
            case MOVE_NO_REPAIR:
            case MOVE_ILLEGAL:
                return lbWait( lb );

            case MOVE_NO_ACCESS_EMBARK:
            case MOVE_NO_TILE:
                return this;

            case ENTER_INDIAN_SETTLEMENT_WITH_MISSIONARY: // Arrived
                break;

            default:
                return lbMove( lb, mt );
        }

        // Establish the mission.
        lbAt( lb );
        Direction d = unit.getTile( ).getDirection( getTarget( ).getTile( ) );
        assert d != null;
        IndianSettlement is = ( IndianSettlement ) getTarget( );
        AIMessage.askEstablishMission( aiUnit, d, is.hasMissionary( ) );
        return ( is.hasMissionary( unit.getOwner( ) ) && unit.isInMission( ) )
                ? lbDone( lb, false, "established" )
                : lbFail( lb, false, "establish" );
    }


    // Serialization

    private static final String TARGET_TAG = "target";


    /**
     * {@inheritDoc}
     */
    @Override
    protected void writeAttributes( FreeColXMLWriter xw ) throws XMLStreamException
    {
        super.writeAttributes( xw );

        if ( target != null )
        {
            xw.writeAttribute( TARGET_TAG, target.getId( ) );
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readAttributes( FreeColXMLReader xr ) throws XMLStreamException
    {
        super.readAttributes( xr );

        target = xr.getLocationAttribute( getGame( ), TARGET_TAG, false );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String getXMLTagName( ) { return getXMLElementTagName( ); }

    /**
     * Gets the tag name of the root element representing this object.
     *
     * @return "missionaryMission".
     */
    public static String getXMLElementTagName( )
    {
        return "missionaryMission";
    }
}
